Targeting SARS-CoV-2 by synthetic dual-acting thiol compounds that inhibit Spike/ACE2 interaction and viral protein production

Redox modulation via a synthetic thiol compound reshapes energy metabolism in endothelial cells and ameliorates angiogenic expression in a co-culture study with activated macrophages

The vascular endothelium is the first interface exposed to circulating compounds and oxidative as well as pro-inflammatory stimuli. Nowadays, cysteine pro-drugs are emerging as new and potential therapies in cardiovascular and inflammatory diseases due to their cytoprotective effects. In this study, the effects of redox modulation by a synthetic thiol compound, i.e., I-152, a precursor of N-acetylcysteine (NAC) and cysteamine (MEA), were evaluated after 6 h and 24 h treatment on human umbilical cord endothelial cell (HUVECs) energy metabolism. Following I-152 treatment, higher cysteine and glutathione (GSH) content were detected via HPLC, in concomitance with I-152 derivatives, i.e., NAC and MEA. Untargeted metabolomics confirmed GSH upregulation and NAC presence in addition to I-152 itself and other metabolites, such as dithiol compound (NACMEAA) and triacetylated I-152. Mass spectrometry revealed that I-152 boosted ATP production, specifically through the mitochondrial OXPHOS, as determined via Seahorse assay without inducing oxidative stress. Additionally, I-152 treatment of HUVECs before co-culture with LPS-stimulated macrophages provided GSH and cysteine sustainment and attenuated the transcription of adhesion molecules as well as iNOS expression. Identifying the impact of redox regulation in physiological conditions and the possible metabolic targets could aid the application of novel thiol-based therapeutics.

TXM peptides inhibit SARS-CoV-2 infection, syncytia formation, and lower inflammatory consequences

After three years of the SARS-CoV-2 pandemic, the search and availability of relatively low-cost benchtop therapeutics for people not at high risk for a severe disease are still ongoing. Although vaccines and new SARS-CoV-2 variants reduce the death toll, the long COVID-19 along with neurologic symptoms can develop and persist even after a mild initial infection. Reinfections, which further increase the risk of sequelae in multiple organ systems as well as the risk of death, continue to require caution. The spike protein of SARS-CoV-2 is an important target for both vaccines and therapeutics. The presence of disulfide bonds in the receptor binding domain (RBD) of the spike protein is essential for its binding to the human ACE2 receptor and cell entry. Here, we demonstrate that thiol-reducing peptides based on the active site of oxidoreductase thioredoxin 1, called thioredoxin mimetic (TXM) peptides, can prevent syncytia formation, SARS-CoV-2 entry into cells, and infection in a mouse model. We also show that TXM peptides inhibit the redox-sensitive HIV pseudotyped viral cell entry. These results support disulfide targeting as a common therapeutic strategy for treating infections caused by viruses using redox-sensitive fusion. Furthermore, TXM peptides exert anti-inflammatory properties by lowering the activation of NF-κB and IRF signaling pathways, mitogen-activated protein kinases (MAPKs) and lipopolysaccharide (LPS)-induced cytokines in mice. The antioxidant and anti-inflammatory effects of the TXM peptides, which also cross the blood-brain barrier, in combination with prevention of viral infections, may provide a beneficial clinical strategy to lower viral infections and mitigate severe consequences of COVID-19.

A synthetic thiol molecule releasing N-acetyl-l-cysteine and cysteamine drives early up-regulation of immunoproteasome subunits in the lymph nodes of mice infected with LP-BM5 leukemia retrovirus

Thiol molecules have been recently re-considered as drug candidates in viral infections because of their ability to induce redox changes which interfere with virus life cycle and modulate the host immune response. Little is known about the molecular mechanisms of their immunomodulatory properties. Here we show that I-152, a thiol molecule metabolized to release N-acetyl-l-cysteine and cysteamine and acting as a pro-glutathione agent, causes early up-regulation of immunoproteasome subunits in the lymph nodes of murine leukemia virus infected mice. This evidence suggests that the immunoproteasome may be modulated by thiol-based compounds with important implications in understanding redox-controlled immunoregulation.

Inhibition of myeloid-derived suppressor cell (MDSC) activity by redox-modulating agents restores T and B cell proliferative responses in murine AIDS

The mechanisms by which myeloid-derived suppressor cells (MDSCs) mediate inhibition prominently include the production of reactive nitrogen species, in particular those generated by inducible nitric oxide synthase (iNOS), and reactive oxygen species. LP-BM5 murine retroviral infection results in a profound immunodeficiency, known as murine AIDS, as well as in increased numbers and activity of monocytic-type MDSCs (M-MDSCs) that suppress both T and B cell responses. While M-MDSCs suppress T cells ex vivo in a fully iNOS/NO-dependent manner, M-MDSC suppression of B cell responses is only partially due to iNOS/NO. This study preliminarily explored the role of two redox-modulating compounds in inhibiting the M-MDSC suppressive activity in LP-BM5 infection. The tested molecules were: I-152 consisting in a conjugate of N-acetyl-cysteine (NAC) and S-acetyl-cysteamine (SMEA) and C4-GSH that is the n-butanoyl glutathione (GSH) derivative. The results show that both molecules, tested in a concentration range between 3 and 20 mM, blocked the M-MDSC suppression of activated B and T cells ex vivo and restored their proliferative capacity in vivo. Ex vivo I-152 blockade of M-MDSC suppressiveness was more significant for T cell (about 70%) while M-MDSC blockade by C4-GSH was preferential for B cell responsiveness (about 60%), which was also confirmed by in vivo investigation. Beyond insights into redox-dependent suppressive effector mechanism(s) of M-MDSCs in LP-BM5 infection, these findings may ultimately be important to identify new immunotherapeutics against infectious diseases.

The influence of redox modulation on hypoxic endothelial cell metabolic and proteomic profiles through a small thiol-based compound tuning glutathione and thioredoxin systems

Reduction in oxygen levels is a key feature in the physiology of the bone marrow (BM) niche where hematopoiesis occurs. The BM niche is a highly vascularized tissue and endothelial cells (ECs) support and regulate blood cell formation from hematopoietic stem cells (HSCs). While in vivo studies are limited, ECs when cultured in vitro at low O2 (<5%), fail to support functional HSC maintenance due to oxidative environment. Therefore, changes in EC redox status induced by antioxidant molecules may lead to alterations in the cellular response to hypoxia likely favoring HSC self-renewal. To evaluate the impact of redox regulation, HUVEC, exposed for 1, 6, and 24 h to 3% O2 were treated with N-(N-acetyl-l-cysteinyl)-S-acetylcysteamine (I-152). Metabolomic analyses revealed that I-152 increased glutathione levels and influenced the metabolic profiles interconnected with the glutathione system and the redox couples NAD(P)+/NAD(P)H. mRNA analysis showed a lowered gene expression of HIF-1α and VEGF following I-152 treatment whereas TRX1 and 2 were stimulated. Accordingly, the proteomic study revealed the redox-dependent upregulation of thioredoxin and peroxiredoxins that, together with the glutathione system, are the main regulators of intracellular ROS. Indeed, a time-dependent ROS production under hypoxia and a quenching effect of the molecule were evidenced. At the secretome level, the molecule downregulated IL-6, MCP-1, and PDGF-bb. These results suggest that redox modulation by I-152 reduces oxidative stress and ROS level in hypoxic ECs and may be a strategy to fine-tune the environment of an in vitro BM niche able to support functional HSC maintenance.

NRF2 Antioxidant Response and Interferon-Stimulated Genes Are Differentially Expressed in Respiratory-Syncytial-Virus- and Rhinovirus-Infected Hospitalized Children

Respiratory diseases caused by respiratory syncytial virus (RSV) and human rhinovirus (HRV) are frequent causes of the hospitalization of children; nonetheless, RSV is responsible for the most severe and life-threatening illnesses. Viral infection triggers an inflammatory response, activating interferon (IFN)-mediated responses, including IFN-stimulated genes (ISG) expression with antiviral and immunomodulatory activities. In parallel, the reactive oxygen species (ROS) production activates nuclear factor erythroid 2-related factor 2 (NRF2), whose antioxidant activity can reduce inflammation by interacting with the NF-kB pathway and the IFN response. To clarify how the interplay of IFN and NRF2 may impact on clinical severity, we enrolled children hospitalized for bronchiolitis and pneumonia, and measured gene expression of type-I and III IFNs, of several ISGs, of NRF2 and antioxidant-related genes, i.e., glucose-6-phosphate dehydrogenase (G6PD), heme oxygenase 1 (HO1), and NAD(P)H dehydrogenase [Quinone] 1 (NQO1) in RSV- (RSV-A N = 33 and RSV-B N = 30) and HRV (N = 22)-positive respiratory samples. NRF2 and HO1 expression is significantly elevated in children with HRV infection compared to RSV (p = 0.012 and p = 0.007, respectively), whereas ISG15 and ISG56 expression is higher in RSV-infected children (p = 0.016 and p = 0.049, respectively). Children admitted to a pediatric intensive care unit (PICU) had reduced NRF2 expression (p = 0.002). These data suggest, for the first time, that lower activation of the NRF2 antioxidant response in RSV-infected infants may contribute to bronchiolitis severity.

Anoxia Rapidly Induces Changes in Expression of a Large and Diverse Set of Genes in Endothelial Cells

Sinusoidal endothelial cells are the predominant vascular surface of the bone marrow and constitute the functional hematopoietic niche where hematopoietic stem and progenitor cells receive cues for self-renewal, survival, and differentiation. In the bone marrow hematopoietic niche, the oxygen tension is usually very low, and this condition affects stem and progenitor cell proliferation and differentiation and other important functions of this region. Here, we have investigated in vitro the response of endothelial cells to a marked decrease in O2 partial pressure to understand how the basal gene expression of some relevant biological factors (i.e., chemokines and interleukins) that are fundamental for the intercellular communication could change in anoxic conditions. Interestingly, mRNA levels of CXCL3, CXCL5, and IL-34 genes are upregulated after anoxia exposure but become downmodulated by sirtuin 6 (SIRT6) overexpression. Indeed, the expression levels of some other genes (such as Leukemia Inhibitory Factor (LIF)) that were not significantly affected by 8 h anoxia exposure become upregulated in the presence of SIRT6. Therefore, SIRT6 mediates also the endothelial cellular response through the modulation of selected genes in an extreme hypoxic condition.